MPLS is a technology to direct digital data packets over computer networks based on path labels, rather than based on network addresses such as IP addresses. Each path label, also known as a “virtual private network” (VPN) label, identifies a path between network nodes, rather than only identifying the endpoints of the packet transmission. Routers of an MPLS network must be enabled to perform label switching to route and forward the packets. Such routers in the interior of an MPLS network are know as “label switch routers,” while such routers at the ingress and egress points of the MPLS network are known as “label edge routers.” Label edge routers discover and interface with non-MPLS networks outside the MPLS network using protocols such as Border Gateway Protocol (BGP). The outside networks can be provider networks, such as a national broadband provider IP networks, in which case the provider's routers are known as provider edge (PE) routers. The use of labels enables each MPLS router to maintain a separate routing and forwarding table instance, known as a virtual routing and forwarding (VRF) table or forwarding information base (FIB), for each of a plurality of tenants of the MPLS.
Generic Routing Encapsulation (GRE) is a point-to-point tunneling protocol in which two peer nodes form the endpoints of the tunnel. GRE is designed to encapsulate network-layer (L3) packets inside IP tunneling packets. Multi-point GRE (mGRE) is a similar protocol with a single endpoint at one side of the tunnel connected to multiple endpoints at the other side of the tunnel. An mGRE tunnel can provide a common link between branch offices that connect to the same VPN.